Some industrial doors have a movable curtain for separating areas within a building or closing off doorways that lead outside. Examples of such doors include planar doors, overhead-storing doors and roll-up doors. Planar doors have curtains that remain generally planar as the curtain, guided by tracks, translates between open and closed positions. Some planar doors have wheels, trolleys or sliding members that couple the curtain to the tracks.
Overhead-storing doors are similar to many conventional garage doors in that overhead-storing doors have guide tracks that curve between a vertical section across the doorway and a horizontal section above the doorway. To open and close the door, the curtain travels to the horizontal and vertical sections, respectively.
A roll-up door comprises a roll-up curtain that when the door is open the curtain is wound about a roller or otherwise coiled above the doorway. To close the door, the curtain unwinds as two vertical tracks guide the curtain across the doorway. Roll-up doors are typically either powered open and closed or are powered open and allowed to fall closed by gravity.
Some roll-up doors have a rigid leading edge provided by a rigid or semi-rigid bar extending horizontally along a lower portion of the curtain. The rigidity of the bar helps keep the curtain within the guide tracks and helps the curtain resist wind and other air pressure differentials that may develop across opposite sides of the door.
Other roll-up doors have a curtain with a relatively soft leading edge. To help keep such a curtain within its guide tracks, as well as keep the curtain taut and square to the doorway, opposite ends of the bottom portion of the curtain can be held in tension by two opposing carriages, trolleys or sliding guide members that are constrained to travel along the tracks. The door's lower leading edge, however, does not necessarily have to be held in tension, especially when the door is not subject to significant pressure differentials.
Industrial doors are often used in warehouses, where the doors are susceptible to being struck by forklifts or other material handling equipment. A collision can also occur when a door accidentally closes upon an obstacle in its path, such as an object or a person. To protect the door and the vehicle from damage and to protect personnel in the area, often some type of breakaway or compliant feature is added to the door. For a door having a rigid reinforcing bar along its leading edge, the bar may be provided with sufficient flexibility and resilience to restorably disengage its tracks during a collision. Doors having a relatively soft leading edge may have sufficient flexibility to absorb an impact. Additionally or alternatively, such doors may have a bottom portion that can be coupled to two opposing guide carriages by way of a breakaway coupling. The coupling releases the curtain from the carriage in response to experiencing a breakaway force, thereby limiting the impact force to a safe level.